Lederer Eleanor DeLand, Khundmiri Syed Jalal, Weinman Edward J
Louisville Veterans Administration Medical Center, Louisville, Kentucky, USA.
J Am Soc Nephrol. 2003 Jul;14(7):1711-9. doi: 10.1097/01.asn.0000072744.67971.21.
Parathyroid hormone (PTH), acting at least in part through a cAMP signaling pathway, regulates three important transporters in the renal proximal convoluted tubule, namely Na-H exchanger 3, Na-K ATPase, and type IIa sodium phosphate cotransporter (NaPi IIa). The regulation of Na-H exchanger 3 by protein kinase A requires a protein co-factor from the sodium-hydrogen exchanger regulatory factor (NHERF) family of proteins (NHERF-1 and NHERF-2). However, the role of NHERF in PTH regulation of Na-K ATPase and NaPi IIa has not been explored. For studying the role of NHERF-1 on PTH regulation of these transporters, wild-type mNHERF-1 (1-355) or mNHERF-1 (1-325) lacking the ezrin-binding domain were expressed in proximal tubule-derived opossum kidney cells. PTH inhibited Na-K ATPase activity in cells expressing wild-type NHERF-1 associated with increased serine phosphorylation of the alpha subunit of the transporter. By contrast, in cells expressing mNHERF (1-325), the phosphorylation of the alpha subunit of Na-K ATPase was blunted and the activity of the transporter was stimulated in response to PTH. Basal sodium-dependent phosphate transport was lower in cells expressing mNHERF-1 (1-325) as compared with cells expressing mNHERF-1 (1-355). Nonetheless, there were no differences in PTH-associated inhibition of the activity or the decrease in membrane expression of the NaPi IIa in any of the cell lines. These experiments document for the first time an association between NHERF-1 and PTH regulation of Na-K ATPase in epithelial cells. These experiments also suggest that the mechanism for retrieval of NaPi IIa transporters from the apical membrane in response to cAMP does not require NHERF.
甲状旁腺激素（PTH）至少部分通过环磷酸腺苷（cAMP）信号通路发挥作用，调节肾近端曲管中的三种重要转运蛋白，即钠氢交换体3（Na-H exchanger 3）、钠钾ATP酶（Na-K ATPase）和IIa型钠磷共转运体（NaPi IIa）。蛋白激酶A对钠氢交换体3的调节需要来自钠氢交换体调节因子（NHERF）蛋白家族（NHERF-1和NHERF-2）的一种蛋白辅助因子。然而，NHERF在PTH对钠钾ATP酶和NaPi IIa的调节中的作用尚未得到研究。为了研究NHERF-1在PTH对这些转运蛋白的调节中的作用，在源自近端小管的负鼠肾细胞中表达了野生型mNHERF-1（1-355）或缺乏埃兹蛋白结合结构域的mNHERF-1（1-325）。PTH抑制了表达野生型NHERF-1的细胞中的钠钾ATP酶活性，这与该转运蛋白α亚基丝氨酸磷酸化增加有关。相比之下，在表达mNHERF（1-325）的细胞中，钠钾ATP酶α亚基的磷酸化减弱，并且该转运蛋白的活性在PTH作用下受到刺激。与表达mNHERF-1（1-355）的细胞相比，表达mNHERF-1（1-325）的细胞中基础钠依赖性磷酸盐转运较低。尽管如此，在任何细胞系中，PTH对NaPi IIa活性的抑制或膜表达的降低均无差异。这些实验首次证明了上皮细胞中NHERF-1与PTH对钠钾ATP酶的调节之间的关联。这些实验还表明，响应cAMP从顶端膜回收NaPi IIa转运蛋白的机制不需要NHERF。
